Chapter 8: Energy and
Metabolism
Why do organisms need energy? How do organisms
manage their energy needs?
Defining terms and issues:


energy and thermodynamics

metabolic reactions and energy transfers
Harvesting and using energy



ATP is the main energy currency in cells

energy harvesting (redox reactions)
Regulating reactions: Enzymes
.
•
Discuss energy conversions and the 1st
and 2nd law of thermodynamics.
–
Be sure to use the terms
•
•
•
•
•
work
potential energy
kinetic energy
entropy
What are Joules (J) and calories (cal)?
.
Chapter 8: Energy and
Metabolism
Why do organisms need energy? How do organisms
manage their energy needs?
Defining terms and issues:


energy and thermodynamics

metabolic reactions and energy transfers
Harvesting and using energy



ATP is the main energy currency in cells

energy harvesting (redox reactions)
Regulating reactions: Enzymes
.
Energy and Thermodynamics

energy for work: change in state or
motion of matter
.
Energy and Thermodynamics
energy for work: change in state or
motion of matter

expressed in Joules or calories


1 kcal = 4.184 kJ
.
Energy and Thermodynamics
energy for work: change in state or
motion of matter

expressed in Joules or calories


1 kcal = 4.184 kJ
energy conversion: energy form change


potential / kinetic
.
Energy and Thermodynamics

potential energy (capacity to
do work)
.
Energy and Thermodynamics

potential energy (capacity to
do work)

kinetic energy (energy of
motion, actively performing
work)

chemical bonds: potential energy

work is required for the processes
of life
.
•
Discuss energy conversions and the 1st
and 2nd law of thermodynamics.
–
Be sure to use the terms
•
•
•
•
•
work
potential energy
kinetic energy
entropy
What are Joules (J) and calories (cal)?
.
Energy and Thermodynamics
Laws of thermodynamics
describe the constraints on
energy usage…
.
•
The laws of thermodynamics are
sometimes stated as:
–
In energy conversions, “You can’t win, and
you can’t break even.”
Explain.
.
Laws of Thermodynamics
First law:


the total amount of energy (+ matter) in a
closed system remains constant
.
Laws of Thermodynamics
First law:


the total amount of energy (+ matter) in a
closed system remains constant

also called conservation of energy
.
Laws of Thermodynamics
First law:


the total amount of energy (+ matter) in a
closed system remains constant

also called conservation of energy

note:

the universe is a closed system

living things are open systems
.
Laws of Thermodynamics
First law:


the total amount of energy (+ matter) in a
closed system remains constant

also called conservation of energy

note:


the universe is a closed system

living things are open systems
“You can’t win.”
.
Laws of Thermodynamics

Second law: in every energy conversion

some energy is converted to heat energy

heat energy is lost to the surroundings

heat energy cannot be used for work
.
Laws of Thermodynamics
Second law: in every energy conversion



some energy is converted to heat energy

heat energy is lost to the surroundings

heat energy cannot be used for work
energy converted to heat in the surroundings
increases entropy (spreading of energy)
.
Laws of Thermodynamics
Second law: in every energy conversion


some energy is converted to heat energy

heat energy is lost to the surroundings

heat energy cannot be used for work

energy converted to heat in the surroundings
increases entropy (spreading of energy)

thus, this law can also be stated as:
Every energy conversion increases the entropy
of the universe.
.
Laws of Thermodynamics
Second law:


Upshot: no energy conversion is 100% efficient

“You can’t break even.”

Just to maintain their current state, organisms
must get a constant influx of energy because of
energy lost in conversions
.
•
The laws of thermodynamics are
sometimes stated as:
–
In energy conversions, “You can’t win, and
you can’t break even.”
Explain.
.
•
Differentiate between:
anabolism and catabolism
exergonic and endergonic reactions
.
Metabolism: anabolism + catabolism
metabolism divided into

anabolism (anabolic reactions)


anabolic reactions are processes that build
complex molecules from simpler ones
.
Metabolism: anabolism + catabolism
metabolism divided into

anabolism (anabolic reactions)


anabolic reactions are processes that build
complex molecules from simpler ones
catabolism (catabolic reactions)


catabolic reactions are processes the break
down complex molecules into simpler ones
.
•
Differentiate between:
anabolism and catabolism
exergonic and endergonic reactions
.
Chemical Reactions and Free Energy
Chemical reactions involve


changes in chemical bonds
.
Chemical Reactions and Free Energy
Chemical reactions involve


changes in chemical bonds

changes in substance concentrations
.
Chemical Reactions and Free Energy
Chemical reactions involve


changes in chemical bonds

changes in substance concentrations

changes in free energy
free energy = energy available to do work in a
chemical reaction (such as: create a chemical
bond)


free energy changes depend on bond energies and
concentrations of reactants and products

bond energy = energy required to break a bond;
value depends on the bond
.
Chemical Reactions and Free Energy
left undisturbed, reactions will reach
dynamic equilibrium when the relative
concentrations of reactants and
products is correct


forward and reverse reaction rates are
equal; concentrations remain constant
.
Chemical Reactions and Free Energy
left undisturbed, reactions will reach
dynamic equilibrium when the relative
concentrations of reactants and
products is correct


forward and reverse reaction rates are
equal; concentrations remain constant

cells manipulate relative concentrations
in many ways so that equilibrium is rare
.
Chemical Reactions and Free Energy
exergonic reactions – the products have less free
energy than reactants


the difference in energy is released and is available to do
work
.
Chemical Reactions and Free Energy
exergonic reactions – the products have less free
energy than reactants


the difference in energy is released and is available to do
work

exergonic reactions are thermodynamically favored; thus,
they are spontaneous, but not necessarily fast (more on
activation energy later)
.
Chemical Reactions and Free Energy

catabolic reactions are usually exergonic

ATP + H2O  ADP + Pi is highly exergonic
.
Chemical Reactions and Free Energy
endergonic reactions – the products have
more free energy than the reactants


the difference in free energy must be supplied
(stored in chemical bonds)
.
Chemical Reactions and Free Energy
endergonic reactions – the products have
more free energy than the reactants


the difference in free energy must be supplied
(stored in chemical bonds)

endergonic reactions are not thermodynamically
favored, so they are not spontaneous
.
Chemical Reactions and Free Energy
.
Chemical Reactions and Free Energy

How to get energy for an endergonic
reaction?
.
Chemical Reactions and Free Energy
How to get energy for an endergonic
reaction?


couple with an exergonic one!
.
Chemical Reactions and Free Energy
How to get energy for an endergonic
reaction?


couple with an exergonic one!

together, the coupled reactions must
have a net exergonic nature
.
Chemical Reactions and Free Energy
How to get energy for an endergonic
reaction?


couple with an exergonic one!

together, the coupled reactions must
have a net exergonic nature

reaction coupling requires that the
reactions share a common intermediate(s)
.
Chemical Reactions and Free Energy
EXAMPLE:
A  B (exergonic)
C  D (endergonic)
.
Chemical Reactions and Free Energy
EXAMPLE:
A  B (exergonic)
C  D (endergonic)
Coupled: A + C  B + D (overall exergonic)
.
Chemical Reactions and Free Energy
EXAMPLE:
A  B (exergonic)
C  D (endergonic)
Coupled: A + C  B + D (overall exergonic)
Actually: A + C  I  B + D
.
Chemical Reactions and Free Energy
EXAMPLE:
A  B (exergonic)
C  D (endergonic)
Coupled: A + C  B + D (overall exergonic)
Actually: A + C  I  B + D

typically, the exergonic reaction in the couple is
ATP + H2O  ADP + Pi

anabolic reactions are usually endergonic
.
Chemical Reactions and Free Energy
EXAMPLE:
A  B (exergonic)
C  D (endergonic)
Coupled: A + C  B + D (overall exergonic)
Actually: A + C  I  B + D

typically, the exergonic reaction in the couple is
ATP + H2O  ADP + Pi

anabolic reactions are usually endergonic
This will be explored in more detail in an example in a bit,
but first some more about ATP…
.
Chapter 8: Energy and
Metabolism
Why do organisms need energy? How do organisms
manage their energy needs?
Defining terms and issues:


energy and thermodynamics

metabolic reactions and energy transfers
Harvesting and using energy



ATP is the main energy currency in cells

energy harvesting (redox reactions)
Regulating reactions: Enzymes
.
Why is ATP so darned important?
What is a phosphorylated intermediate?
How much ATP is in a cell at any given time?
Why must cells keep a high ATP/ADP ratio?
.
ATP is the main energy currency in cells

One way that organisms manage
their energy needs is to use ATP as a
ready energy source for many
reactions.
.
ATP is the main energy currency in cells

ATP – nucleotide with adenine base,
ribose sugar, and a chain of 3
phosphate groups
.
ATP is the main energy currency in cells

last two phosphate groups are joined
to the chain by unstable bonds;
breaking these bonds is relatively
easy and releases energy; thus:
.
ATP is the main energy currency in cells

hydrolysis of ATP to ADP and
inorganic phosphate (Pi) releases
energy
ATP + H2O  ADP + Pi
.
ATP is the main energy currency in cells
hydrolysis of ATP to ADP and
inorganic phosphate (Pi) releases
energy

ATP + H2O  ADP + Pi
the amount of energy released


depends in part on concentrations of
reactants and products

is generally ~30 kJ/mol
.
ATP is the main energy currency in cells

Intermediates when ATP hydrolysis is coupled to
a reaction to provide energy
.
ATP is the main energy currency in cells
Intermediates when ATP hydrolysis is coupled to
a reaction to provide energy


often phosphorylated compounds
glucose
glucose-6-phosphate
.
ATP is the main energy currency in cells
Intermediates when ATP hydrolysis is coupled to
a reaction to provide energy


often phosphorylated compounds

the inorganic phosphate is transferred onto another
compound rather than being immediately released
glucose
glucose-6-phosphate
.
ATP is the main energy currency in cells
Intermediates when ATP hydrolysis is coupled to
a reaction to provide energy


often phosphorylated compounds

the inorganic phosphate is transferred onto another
compound rather than being immediately released

a phosphorylated compound is in a higher energy state
glucose
glucose-6-phosphate
.
ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol)
coupled:
glucose + fructose + ATP + H2O  sucrose + H2O + ADP + Pi
simplified:
glucose + fructose + ATP  sucrose +ADP + Pi
with intermediates:
glucose + fructose + ATP + H2O  glucose-P + fructose + ADP 
sucrose + H2O + ADP + Pi (net exergonic, releases ~3 kJ/mol)
.
ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol)
.
ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol)
coupled:
glucose + fructose + ATP + H2O  sucrose + H2O + ADP + Pi
.
ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol)
coupled:
glucose + fructose + ATP + H2O  sucrose + H2O + ADP + Pi
simplified:
glucose + fructose + ATP  sucrose +ADP + Pi
.
ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol)
coupled:
glucose + fructose + ATP + H2O  sucrose + H2O + ADP + Pi
simplified:
glucose + fructose + ATP  sucrose +ADP + Pi
with intermediates:
glucose + fructose + ATP + H2O  glucose-P + fructose + ADP 
sucrose + H2O + ADP + Pi (net exergonic, releases ~3 kJ/mol)
.
ATP is the main energy currency in cells

Thus, energy transfer in cellular reactions
is often accomplished through transfer of
a phosphate group from ATP
.
ATP is the main energy currency in cells
Making ATP involves an endergonic
condensation reaction


reverse of an exergonic reaction is always
endergonic
ADP + Pi  ATP + H2O
.
ATP is the main energy currency in cells
Making ATP involves an endergonic
condensation reaction


reverse of an exergonic reaction is always
endergonic
ADP + Pi  ATP + H2O

endergonic, usually requires more than ~30
kJ/mol
.
ATP is the main energy currency in cells
Making ATP involves an endergonic
condensation reaction


reverse of an exergonic reaction is always
endergonic
ADP + Pi  ATP + H2O

endergonic, usually requires more than ~30
kJ/mol

must be coupled with an exergonic reaction;
typically from a catabolic pathway (more on that
later)
.
ATP is the main energy currency in cells

Overall, ATP is typically created in
catabolic reactions and used in
anabolic reactions, linking those
aspects of metabolism
.
ATP is the main energy currency in cells
Cells maintain high levels of ATP relative to ADP


maximizes energy available from hydrolysis of ATP
.
ATP is the main energy currency in cells
Cells maintain high levels of ATP relative to ADP


maximizes energy available from hydrolysis of ATP

ratio typically greater than 10 ATP: 1 ADP
.
ATP is the main energy currency in cells
Overall concentration of ATP still very low


supply typically only enough for a few seconds at
best
.
ATP is the main energy currency in cells
Overall concentration of ATP still very low


supply typically only enough for a few seconds at
best

instability prevents stockpiling
.
ATP is the main energy currency in cells
Overall concentration of ATP still very low


supply typically only enough for a few seconds at
best

instability prevents stockpiling

must be constantly produced

in a typical cell, the rate of use and production of ATP is
about 10 million molecules per second

resting human has less than 1 g of ATP at any given time
but uses about 45 kg per day
.
Why is ATP so darned important?
What is a phosphorylated intermediate?
How much ATP is in a cell at any given time?
Why must cells keep a high ATP/ADP ratio?
.
•
What are redox reactions used for in
cells?
•
How (generally) can you tell which of
two similar compounds is reduced and
which is oxidized?
•
Give some examples of compounds
commonly used in redox reactions in
cells.
.
Redox reactions are also used for
energy transfer
Redox reactions are used to harvest energy from some chemicals.
The acceptors of that energy typically cannot be used directly as
energy currency.
.
Redox reactions are also used for
energy transfer
Redox reactions are used to harvest energy from some chemicals.
The acceptors of that energy typically cannot be used directly as
energy currency.

Electrons can also be used for energy transfer
.
Redox reactions are also used for
energy transfer
Redox reactions are used to harvest energy from some chemicals.
The acceptors of that energy typically cannot be used directly as
energy currency.
Electrons can also be used for energy transfer


Redox reactions: recall reduction, gain electrons;
oxidation, lose electrons; both occur simultaneously in cells
(generally no free electrons in cells)
.
Redox reactions are also used for
energy transfer
Redox reactions are used to harvest energy from some chemicals.
The acceptors of that energy typically cannot be used directly as energy
currency.
Electrons can also be used for energy transfer


Redox reactions: recall reduction, gain electrons; oxidation,
lose electrons; both occur simultaneously in cells (generally no
free electrons in cells)

Typically, the oxidized substance gives up energy with the
electron, the reduced substance gains energy with the electron
.
08.04 Redox Reactions
Slide number: 6
Loss of electron (oxidation)
o
A
o
+
B
e–
A
_
+
B
A*
Gain of electron (reduction)
Low energy
High energy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
B*
Redox reactions are also used for
energy transfer
chain of redox reactions / electron transfers common


more on electron transport chains later
.
Redox reactions are also used for
energy transfer
chain of redox reactions / electron transfers common


more on electron transport chains later
each electron transfer releases free energy


free energy can be used for other chemical reactions
.
Redox reactions are also used for
energy transfer
chain of redox reactions / electron transfers common


more on electron transport chains later
each electron transfer releases free energy


free energy can be used for other chemical reactions
proton often removed as well


if so, equivalent of a hydrogen atom is transferred
.
Redox reactions are also used for
energy transfer
Catabolism typically involves:


removal of hydrogen atoms from nutrients
(such as carbohydrates)

transfer of the protons and electrons to
intermediate electron acceptors
.
Redox reactions are also used for
energy transfer

intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+)
.
Redox reactions are also used for
energy transfer

intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+)

Use XH2 to represent a nutrient molecule:
XH2 + NAD+  X + NADH + H+
.
Redox reactions are also used for
energy transfer

intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+)

Use XH2 to represent a nutrient molecule:
XH2 + NAD+  X + NADH + H+

Often, the reduced form is just called NADH
.
Redox reactions are also used for
energy transfer

Reduced state stores energy, which
is partially released as free energy
when NADH is oxidized
.
Redox reactions are also used for
energy transfer

Reduced state stores energy, which
is partially released as free energy
when NADH is oxidized

The free energy usually winds up
being used to make ATP
.
Redox reactions are also used for
energy transfer
Other commonly used acceptors are
NADP+, FAD, and cytochromes


NADP+/NADPH – important in
photosynthesis

FAD/FADH2 – flavin adenine dinucleotide

Cytochromes – small iron-containing
proteins; iron serves as electron acceptor
.
•
What are redox reactions used for in
cells?
•
How (generally) can you tell which of
two similar compounds is reduced and
which is oxidized?
•
Give some examples of compounds
commonly used in redox reactions in
cells.
.
Chapter 8: Energy and
Metabolism
Why do organisms need energy? How do organisms
manage their energy needs?
Defining terms and issues:


energy and thermodynamics

metabolic reactions and energy transfers
Harvesting and using energy



ATP is the main energy currency in cells

energy harvesting (redox reactions)
Regulating reactions: Enzymes
.
•
What do enzymes do for cells, and how
do they do it?
–
Be sure to use the following terms:
•
catalyst (or catalyze)
•
activation energy
•
enzyme-substrate complex
•
active site
•
induced fit
.
Enzymes

Manipulation of reactions is essential
to and largely defining of life.
.
Enzymes

Manipulation of reactions is essential
to and largely defining of life.

Organisms use enzymes to
manipulate the speed of reactions.
.
Enzymes

Manipulation of reactions is essential
to and largely defining of life.

Organisms use enzymes to
manipulate the speed of reactions.

Understanding life requires
understanding how enzymes work.
.
Enzymes
Enzymes regulate chemical reactions in living organisms

An enzyme is an organic molecule (typically a protein)
that acts as a catalyst
.
Enzymes
Enzymes regulate chemical reactions in living organisms
An enzyme is an organic molecule (typically a protein)
that acts as a catalyst


catalyst –increases the rate of a chemical reaction
without being consumed in the reaction (the catalyst
recycles back to its original state)
.
Enzymes
Enzymes regulate chemical reactions in living organisms
An enzyme is an organic molecule (typically a protein)
that acts as a catalyst


catalyst –increases the rate of a chemical reaction
without being consumed in the reaction (the catalyst
recycles back to its original state)

enzymes (catalysts) only alter reaction rate;
thermodynamics still governs whether the reaction
can occur
.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 8.9 (TEArt)
1
The substrate,
sucrose, consists
of glucose and
fructose bonded
together.
2 The substrate
binds to the
enzyme, forming
an enzyme-
substrate
complex.
Bond
Enzyme
Fructose
4 Products are
released, and
the enzyme is
free to bind
other
substrates.
3 The binding of
the substrate
and enzyme
places stress on
the glucosefructose bond,
and the bond
breaks.
H2O
Active site
Glucose
08.09 Enzyme Catalytic Cycle
Slide number: 2
1 The substrate, sucrose, consists
of glucose and fructose bonded
together.
Bond
Active site
Enzyme
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
08.09 Enzyme Catalytic Cycle
Slide number: 3
1 The substrate, sucrose, consists
of glucose and fructose bonded
together.
Bond
Active site
Enzyme
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
08.09 Enzyme Catalytic Cycle
Slide number: 4
1 The substrate, sucrose, consists
of glucose and fructose bonded
together.
2 The substrate binds to the
enzyme, forming an enzymesubstrate complex.
Bond
Active site
Enzyme
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
08.09 Enzyme Catalytic Cycle
Slide number: 5
1 The substrate, sucrose, consists
of glucose and fructose bonded
together.
2 The substrate binds to the
enzyme, forming an enzymesubstrate complex.
Bond
H2O
Active site
Enzyme
3 The binding of the substrate
and enzyme places stress
on the glucose-fructose
bond, and the bond breaks.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
08.09 Enzyme Catalytic Cycle
Slide number: 6
1 The substrate, sucrose, consists
Glucose
Fructose
of glucose and fructose bonded
together.
2 The substrate binds to the
enzyme, forming an enzymesubstrate complex.
Bond
4 Products are
H2O
released, and the
enzyme is free to
bind other
substrates.
3 The binding of the substrate
Active site
and enzyme places stress
on the glucose-fructose
Enzyme
bond, and the bond breaks.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Enzymes
work by lowering activation energy of a reaction


all reactions have a required energy of activation
.
Enzymes
work by lowering activation energy of a reaction

all reactions have a required energy of activation


energy required to break existing bonds and bring reactants together
.
Enzymes
work by lowering activation energy of a reaction

all reactions have a required energy of activation


energy required to break existing bonds and bring reactants together

must be supplied in some way before the reaction can proceed
.
Enzymes
activation energy


catalysts greatly reduce the activation energy
requirement, making it easier for a reaction to occur
.
Enzymes
Enzymes lower activation energy by forming a complex with the
substrate(s)


the ability to form an enzyme-substrate complex is highly
dependent on the shape of the enzyme
.
Enzymes
Enzymes lower activation energy by forming a complex with the
substrate(s)


the ability to form an enzyme-substrate complex is highly
dependent on the shape of the enzyme

the site where the substrate(s) binds to the enzyme is called the
active site
.
Enzymes
Enzymes lower activation energy by forming a complex with the
substrate(s)


the ability to form an enzyme-substrate complex is highly
dependent on the shape of the enzyme

the site where the substrate(s) binds to the enzyme is called the
active site

when the enzyme-substrate complex forms, there are typically shape
changes in the enzyme and substrate(s) – called induced fit
.
Enzymes

ES complex typically very unstable
.
Enzymes
ES complex typically very unstable


short-lived
.
Enzymes
ES complex typically very unstable


short-lived

breaks down into released product(s) and a
free enzyme that is ready to be reused
.
Enzymes
ES complex typically very unstable



short-lived

breaks down into released product(s) and a
free enzyme that is ready to be reused
overall:
enzyme + substrate(s)  ES complex  enzyme + product(s)
.
•
What do enzymes do for cells, and how
do they do it?
–
Be sure to use the following terms:
•
catalyst (or catalyze)
•
activation energy
•
enzyme-substrate complex
•
active site
•
induced fit
.
•
What are the four main things that
enzymes do to lower activation energy?
.
Enzymes

reduction in activation energy is due primarily to four things:
.
Enzymes
reduction in activation energy is due primarily to four things:


an enzyme holds reactants (substrates) close together in the
right orientation for the reaction, which reduces the reliance
on random collisions
.
Enzymes
reduction in activation energy is due primarily to four things:


an enzyme holds reactants (substrates) close together in the
right orientation for the reaction, which reduces the reliance
on random collisions

an enzyme may put a “strain” on existing bonds, making them
easier to break
.
Enzymes
reduction in activation energy is due primarily to four things:


an enzyme holds reactants (substrates) close together in the
right orientation for the reaction, which reduces the reliance
on random collisions

an enzyme may put a “strain” on existing bonds, making them
easier to break

an enzyme provides a “microenvironment” that is more
chemically suited to the reaction
.
Enzymes
reduction in activation energy is due primarily to four things:


an enzyme holds reactants (substrates) close together in the
right orientation for the reaction, which reduces the reliance
on random collisions

an enzyme may put a “strain” on existing bonds, making them
easier to break

an enzyme provides a “microenvironment” that is more
chemically suited to the reaction

sometimes the active site of the enzyme itself is directly
involved in the reaction during the transition states
.
Enzymes
enzyme + substrate(s)  ES complex  enzyme + product(s)
.
•
What are the four main things that
enzymes do to lower activation energy?
.
•
How are enzymes named (what suffixes
indicate an enzyme)?
.
Enzymes
Enzyme names


many names give some indication of substrate
.
Enzymes
Enzyme names


many names give some indication of substrate

most enzyme names end in –ase (example:
sucrase)
.
Enzymes
Enzyme names


many names give some indication of substrate

most enzyme names end in –ase (example:
sucrase)

some end in –zyme (example: lysozyme)
.
Enzymes
Enzyme names


many names give some indication of substrate

most enzyme names end in –ase (example:
sucrase)

some end in –zyme (example: lysozyme)

some traditional names are less indicative of
enzyme function (examples: pepsin, trypsin)
.
Enzymes
Enzymes are generally highly specific


overall shape as well as spatial arrangements in
the active site limit what enzyme-substrate
complexes can readily form
.
Enzymes
the amount of specificity depends on the particular
enzyme


example of high specificity: sucrase splits sucrose,
not other disaccharides
.
Enzymes
the amount of specificity depends on the particular
enzyme


example of high specificity: sucrase splits sucrose,
not other disaccharides

example of low specificity: lipase splits variety of
fatty acids from glycerol
.
Enzymes
enzymes are classified by the kind of reaction they catalyze

The International Union of Biochemistry and Molecular Biology has
developed a nomenclature for enzymes; the top-level
classification is






Oxidoreductases: catalyze oxidation/reduction reactions
Transferases: transfer a functional group (e.g. a methyl or
phosphate group)
Hydrolases: catalyze the hydrolysis of various bonds
Lyases: cleave various bonds by means other than hydrolysis and
oxidation
Isomerases: catalyze isomerization changes within a single
molecule
Ligases: join two molecules with covalent bonds
The complete nomenclature can be browsed at
http://www.chem.qmul.ac.uk/iubmb/enzyme/
.
•
How are enzymes named (what suffixes
indicate an enzyme)?
.
•
Explain the terms cofactor, apoenzyme,
and coenzyme.
.
Enzymes

Many enzymes require additional chemical
components (cofactors) to function
.
Enzymes
Many enzymes require additional chemical
components (cofactors) to function


apoenzyme + cofactor  active enzyme
(bound together)
.
Enzymes
Many enzymes require additional chemical
components (cofactors) to function


apoenzyme + cofactor  active enzyme
(bound together)

alone, an apoenzyme or a cofactor has little
if any catalytic activity
.
Enzymes
Many enzymes require additional chemical
components (cofactors) to function


apoenzyme + cofactor  active enzyme
(bound together)

alone, an apoenzyme or a cofactor has little
if any catalytic activity

cofactors may or may not be changed by the
reaction
.
Enzymes
cofactors can be organic or inorganic

organic examples (coenzymes):


ADP, NAD+, NADP+, FAD

typically changed by the catalyzed reaction
.
Enzymes
cofactors can be organic or inorganic

organic examples (coenzymes):


ADP, NAD+, NADP+, FAD

typically changed by the catalyzed reaction
inorganic examples:


metal ions like Ca2+, Mg2+, Fe3+, etc.

typically not changed by the catalyzed reaction
.
Enzymes
cofactors can be organic or inorganic

organic examples (coenzymes):


ADP, NAD+, NADP+, FAD

typically changed by the catalyzed reaction
inorganic examples:



metal ions like Ca2+, Mg2+, Fe3+, etc.

typically not changed by the catalyzed reaction
most vitamins are coenzymes or part of coenzymes,
or are used for making coenzymes
.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 8.3 (TEArt)
Energy-rich molecule
Enzyme
H
H
NAD+
NAD+
1. Enzymes that harvest
hydrogen atoms have a
binding site for NAD+
located near another
binding site. NAD+ and
an energy-rich
molecule bind to
the enzyme.
H
NAD+
Product
NAD H
2. In an oxidationreduction reaction,
a hydrogen atom
is transferred to
NAD+, forming
NADH.
NAD H
3. NADH then
diffuses away and
is available to
other molecules.
Fig. 8.A
.
•
Explain the terms cofactor, apoenzyme,
and coenzyme.
.
•
Discuss the effects of temperature and
pH on enzyme activity.
.
Enzymes are most active under optimal conditions
each enzyme has an optimal temperature


most effective as a catalyst at the optimal temperature
.
Enzymes are most active under optimal conditions
each enzyme has an optimal temperature


most effective as a catalyst at the optimal temperature

rate of drop-off in effectiveness away from optimal
temperature depends on the enzyme
.
Enzymes are most active under optimal conditions
each enzyme has an optimal temperature


most effective as a catalyst at the optimal temperature

rate of drop-off in effectiveness away from optimal
temperature depends on the enzyme

high temperatures tend to denature enzymes
.
Enzymes are most active under optimal conditions
each enzyme has an optimal temperature


most effective as a catalyst at the optimal temperature

rate of drop-off in effectiveness away from optimal
temperature depends on the enzyme

high temperatures tend to denature enzymes

human enzymes have temperature optima near human body
temperature (37°C)
.
Enzymes are most active under optimal conditions
each enzyme has an optimal pH


again, most effective at the optimum; drop-off varies
.
Enzymes are most active under optimal conditions
each enzyme has an optimal pH


again, most effective at the optimum; drop-off varies

extremes of pH tend to denature enzymes
.
Enzymes are most active under optimal conditions
each enzyme has an optimal pH


again, most effective at the optimum; drop-off varies

extremes of pH tend to denature enzymes

a particular organism shows more variety in enzyme pH
optima than in temperature optima, but most of its enzymes
will still be optimal at the pH normally found in the cytosol of its
cells
.
•
Discuss the effects of temperature and
pH on enzyme activity.
.
•
What is a metabolic pathway?
.
Enzymes

Metabolic pathways use organized “teams” of
enzymes

the products of one reaction often serve as
substrates for the next reaction
.
Enzymes

Metabolic pathways use organized “teams” of
enzymes

the products of one reaction often serve as
substrates for the next reaction

removing products (by having them participate
the “next reaction”) improves reaction rate
(avoids equilibrium)
.
Enzymes

Metabolic pathways use organized “teams” of
enzymes

the products of one reaction often serve as
substrates for the next reaction

removing products (by having them participate
the “next reaction”) improves reaction rate
(avoids equilibrium)

multiple metabolic pathways exit in cells,
overlapping in some areas and diverging in
others
.
Fig. 8.15
.
•
What is a metabolic pathway?
.
•
How do cells regulate enzyme activity?
–
Include the terms:
•
•
•
•
•
inhibitors
activators
allosteric site
feedback inhibition
Also, differentiate between:
–
–
irreversible and reversible inhibition
competitive and noncompetitive inhibition
.
Enzymes
Cells can regulate enzyme activity to control reactions


increase substrate amount  increase reaction rate
(up to saturation of available enzyme molecules)
.
Enzymes
Cells can regulate enzyme activity to control reactions


increase substrate amount  increase reaction rate
(up to saturation of available enzyme molecules)

increase enzyme amount  increase reaction rate
(as long as substrate amount > enzyme amount)
.
Enzymes
Cells can regulate enzyme activity to control reactions


increase substrate amount  increase reaction rate
(up to saturation of available enzyme molecules)

increase enzyme amount  increase reaction rate
(as long as substrate amount > enzyme amount)

compartmentation of the enzyme, substrate, and
products can help control reaction rate
.
Rate of reaction
Rate of reaction
When substrate concentration >> enzyme concentration….
Enzyme concentration
(a)
Substrate concentration
(b)
Cells can regulate enzyme
activity to control reactions

inhibitors and activators
of enzymes

activators allow or
enhance catalytic activity
.
Cells can regulate enzyme
activity to control reactions

inhibitors and activators
of enzymes

activators allow or
enhance catalytic activity

inhibitors reduce or
eliminate catalytic activity
.
Cells can regulate enzyme
activity to control reactions

inhibitors and activators
of enzymes

activators allow or
enhance catalytic activity

inhibitors reduce or
eliminate catalytic activity

sometime, this uses an
allosteric site – a receptor
site on an enzyme where
an inhibitor or activator can
bind
.
Cells can regulate enzyme
activity to control reactions
a common example of
allosteric control is
feedback inhibition


the last product in a
metabolic pathway binds
to an allosteric site of an
enzyme in an early step
of the pathway (often the
first)

this product inhibits
activity of the enzyme
.
Threonine
Enzyme #1
(Threonine
deaminase)
-Ketobutyrate
Enzyme #2
-Aceto--hydroxybutyrate
Enzyme #3
Feedback inhibition
,b-Dihydroxy-b-methylvalerate
(Isoleucine inhibits
enzyme #1)
Enzyme #4
-Keto-b-methylvalerate
Enzyme #5
Isoleucine
Fig. 9.20
.
Cells can regulate enzyme
activity to control reactions

irreversible inhibition – enzyme is
permanently inactivated or destroyed;
includes many drugs and toxins
.
Cells can regulate enzyme
activity to control reactions

irreversible inhibition – enzyme is
permanently inactivated or destroyed;
includes many drugs and toxins

reversible inhibition – if inhibitor is
removed, the enzyme activity can be
recovered
.
Cells can regulate enzyme
activity to control reactions

reversible inhibition – if
inhibitor is removed, the
enzyme activity can be
recovered

competitive inhibition –
inhibitor is similar in structure
to a substrate; competes with
substrate for binding to the
active site
.
Cells can regulate enzyme
activity to control reactions

reversible inhibition – if
inhibitor is removed, the
enzyme activity can be
recovered

competitive inhibition –
inhibitor is similar in structure
to a substrate; competes with
substrate for binding to the
active site

noncompetitive inhibition –
binds at allosteric site, alters
enzyme shape to make
active site unavailable
.
•
How do cells regulate enzyme activity?
–
Include the terms:
•
•
•
•
•
inhibitors
activators
allosteric site
feedback inhibition
Also, differentiate between:
–
–
irreversible and reversible inhibition
competitive and noncompetitive inhibition
.